The intermission lasted more than a half-hour Saturday night in St. Mark's Episcopal Church on Capitol Hill. Two harpsichords, suffering from the evening's humidity even more than the audience, had to be retuned before the program could conclude with J.S. Bach's Concerto in C, BWV 1061, where they do most of the work.

Fortunately for Bach and for the Plum Chamber Consort, the (finally) well-tempered harpsichords were in excellent hands--Lois Pipkin and James Weaver, two artists who match fine technique with a precise sense of baroque style. The show was all theirs in this concerto, where the orchestra is completely silent during the slow movement and makes only a rudimentary contribution to the opening allegro and concluding fugue. They made it the highlight of the evening.

Earlier, flutist Penelope Fischer gave a charmingly idiomatic account of Carl Philipp Emanuel Bach's Flute Concerto in G, playing a wooden baroque flute modeled on one made in Brussels around 1745. This instrument, gentler in tone than its modern counterpart, blended beautifully with the sound of the small orchestra (six strings and harpsichord), producing exquisite sound textures. Fischer played it stylishly and with lyric grace.

The Plum's use of 18th-century instruments in their original condition makes its concerts a special kind of experience but also involves problems. The authentic pitch of these instruments is somewhat lower than today's standard, and this can make the ear uneasy: are the violins out of tune? In fact, by any pitch standard, they were sometimes, particularly in the opening work, J.S. Bach's Violin Concerto in A Minor.